Bill Xia, President of Dynamic Internet Technology says to South China Morning Post-
"It believes that incident was resulted of a system malfunction or operator mistake which redirected a range of Internet domains to the company’s site, which is actually banned in China."The huge amount of the redirected traffic on the website of Dynamic Internet Technology's security system to shut down the site, also with the many of others sites too, which is just showing the blank page.
This issue was lasted for a hour but it was more at rural areas. Net.cn, Internet Service Provider owned by Alibaba says that the incident was known issue.
Some points out that whether the sites were actually down. As some of the China internet users who were using VPN to access the web didn't find any issue like this.
Compuware, IT performance company says that, issues seemingly related to the DNS, which could explain why VPN users were unaffected.
The actually reason behind the issue is not been cleared, or this may be the part of the Internet hacktivist group.